U.S. patent number 6,783,689 [Application Number 10/145,605] was granted by the patent office on 2004-08-31 for method of forming pillars in a fully integrated thermal inkjet printhead.
This patent grant is currently assigned to Hewlett-Packard Development Company, L.P.. Invention is credited to Naoto Kawamura, David R Thomas, David J Waller, Timothy L. Weber.
United States Patent |
6,783,689 |
Kawamura , et al. |
August 31, 2004 |
**Please see images for:
( Certificate of Correction ) ** |
Method of forming pillars in a fully integrated thermal inkjet
printhead
Abstract
Pillars are formed in a fully integrated thermal inkjet
printhead to prevent particles from entering into a nozzle chamber
along an ink refill channel. The pillars are formed after a step of
applying a thin film structure to a substrate. At one step, pits
are etched through the thin film structure. At another step,
material for an orifice layer is deposited into the pits. At
another step, a firing chamber is etched into the orifice layer. At
another step, a trench is etched into the backside of the wafer in
the vicinity of the filled pits. The material filling each pit is
not removed and remains in place to define the respective pillars.
Two or more pillars are formed within the trench for each inkjet
nozzle chamber. Alternatively pillars are formed by depositing
material into the underside trench and performing photoimaging
processes.
Inventors: |
Kawamura; Naoto (Corvallis,
OR), Thomas; David R (Corvallis, OR), Waller; David J
(Corvallis, OR), Weber; Timothy L. (Corvallis, OR) |
Assignee: |
Hewlett-Packard Development
Company, L.P. (Houston, TX)
|
Family
ID: |
22651595 |
Appl.
No.: |
10/145,605 |
Filed: |
May 10, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
668627 |
Sep 22, 2000 |
6641744 |
|
|
|
178194 |
Oct 23, 1998 |
6309054 |
|
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Current U.S.
Class: |
216/27; 216/17;
216/19; 347/65 |
Current CPC
Class: |
B41J
2/14145 (20130101); B41J 2/1603 (20130101); B41J
2/1626 (20130101); B41J 2/1631 (20130101); B41J
2/164 (20130101); B41J 2/1645 (20130101); B41J
2002/14403 (20130101); Y10T 29/49401 (20150115); Y10T
29/49083 (20150115) |
Current International
Class: |
B41J
2/14 (20060101); B41J 2/16 (20060101); B41J
002/04 () |
Field of
Search: |
;216/17,19,27
;347/65,63 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Norton; Nadine G.
Assistant Examiner: Ahmed; Shamim
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a divisional of U.S. Pat. application Ser. No.
09/668,627 filed on Sep. 22, 2000 now U.S. Pat. No. 6,641,744 which
is a division of U.S. Pat. application Ser. No. 09/178,194 filed
Oct. 23, 1998 now U.S. Pat. No. 6,309,054.
This invention is related to the subject matter disclosed in
commonly--assigned U.S. patent application Ser. No. 09/033,987
filed Mar. 3, 1998 for "Direct Imaging Polymer Fluid Jet Orifice,"
of Chen at al., the content of which is incorporated herein by
reference and made a part hereof.
Claims
What is claimed is:
1. A method to form a pillar in a printhead comprising: applying a
thin flu structure to a first surface of a substrate; etching a
trench into a second surface of the substrate opposite the first
surface; applying photoimageable material within the trench; and
removing a portion of the photoimageable material leaving a
plurality of pillars protruding within the trench.
2. The method of claim 1 further comprising: applying an orifice
layer to the thin film structure opposite the substrate; forming a
nozzle amber within the orifice layer; and forming an inlet opening
which extends from the nozzle chamber through the thin film
structure.
3. The method of claim 2, in which applying the orifice layer,
forming the nozzle chamber and forming the inlet opening occur
prior to applying photoimageable material.
4. The method of claim 2, in which applying the orifice layer,
forming the nozzle chamber and forming the inlet opening occur
prior to etching the trench.
5. The method of claim 1, in which etching the trench into the
second surface of the substrate includes etching a trench less than
all the way through the substrate, and in which applying
photoimageable material includes applying photoimageable material
within the trench to an exposed portion of the substrate.
6. The method of claim 2 further comprising flowing ink into the
trench and through the inlet opening into the nozzle chamber to
refill a nozzle chamber.
7. The method of claim 6 further comprising blocking, with at least
one of the plural of pillars, a particle carried by the ink,
wherein the particle is kept away from the inlet opening allowing
ink to flow into the nozzle chamber.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to a method for fabricating a
fully integrated (monolithic) inkjet printhead, and more
particularly to a method for forming pillars within the printhead
to reduce particle clogging of ink refill channels.
A thermal inkjet printhead is part of an inkjet pen. The inkjet pen
typically includes a reservoir for storing ink, a casing and the
inkjet printhead. The printhead includes a plurality of nozzles for
ejecting ink. A nozzle operates by rapidly heating a small volume
of ink in a nozzle chamber. The heating causes the ink to vaporize
and be ejected through an orifice onto a print medium, (e.g., a
sheet of paper). Properly sequenced ejection of ink from numerous
nozzles arranged in a pattern causes characters, symbols or other
graphics to be printed on the print medium as the printhead moves
relative to the print medium.
The inkjet printhead includes one or more refill channels for
carrying ink from the reservoir into respective nozzle chambers.
According to one conventional fabrication methodology, a nozzle
chamber is defined in a barrier layer applied to a substrate. An
orifice plate is applied to the barrier layer. The substrate forms
a floor of the firing chamber (along with a firing resistor), while
the orifice plate forms a ceiling to the firing chamber. According
to another conventional fabrication methodology, a fully
integrated, or monolithic, printhead of inkjet nozzles is formed
using photoimaging techniques similar to those used in
semiconductor device manufacturing. The fully integrated thermal
(FIT) inkjet printhead includes a thin film layer formed of various
passivation, insulation, resistive and conductive layers applied to
a silicon wafer.
One problem which affects print quality is clogging of the ink
refill channels. Once a nozzle chamber is fired ejecting a drop of
ink, ink flows from the reservoir through the ink refill channels
into the nozzle chambers. Typically, the ink is stored within a
porous material filling the reservoir to achieve fluid retention
and fluid pressure benefits. A disadvantage of the porous material,
however, is that particles are occasionally disengaged and carried
by the ink into the ink refill channels. Even for devices without a
porous material in the ink reservoir, particles remaining from
manufacturing processes may be carried by ink to the refill
channels. Such porous material particles or leftover manufacturing
process particles can become lodged and block a refill channel.
Blocking of a refill channel can cause premature failure of an
inkjet firing chamber, or cause ink starvation of the inkjet firing
chamber. The failure of a nozzle to eject an ink droplet can harm
print quality. Redundant nozzles have been proposed and implemented
as one solution to this problem.
Pillars and barrier islands have been proposed to capture particles
and provide redundant pathways leading to the nozzle chambers. U.S.
Pat. No. 5,463,413 issued Oct. 31, 1995 to Ho et al. for "Internal
support for Top-Shooter Thermal Inkjet Printhead" discloses pillars
for a printhead formed by a substrate, barrier layer and orifice
plate. U.S. Pat. No. 5,734,399 issued Mar. 31, 1998 to Weber et al.
for "Particle Tolerant Inkjet Printhead Architecture" discloses
barrier islands for a printhead also formed by a substrate, barrier
layer and orifice plate. Both of these patents disclose forming the
pillars or barrier islands in the barrier layer before applying the
orifice plate.
SUMMARY OF THE INVENTION
According to the invention, pillars are formed in a fully
integrated thermal inkjet printhead to prevent particles from
entering into a nozzle chamber along an ink refill channel. Ink can
flow into the nozzle chamber even in the presence of a particle
blocking one of multiple ink refill channels leading to the nozzle
chamber.
According to one aspect of the invention, the pillars are formed
after a step of applying a thin film structure to a printhead
substrate. The thin film structure includes various passivation,
insulation, resistive and conductive layers applied to the
substrate using photoimaging and deposition techniques.
According to another aspect of the invention, pits are etched
through the thin film structure into the wafer at one step. Ink
feed holes are etched through the thin film structure and into the
wafer, concurrently or during a separate step. At another step,
material for an orifice layer is deposited into the pits and holes
and onto the thin film structure. At another step, a firing chamber
is etched into the orifice layer. During this step material is
removed from the ink feed holes. At another step, a trench is
etched into the backside of the wafer in the vicinity of the filled
pits and the ink feed holes. The material filling each pit is not
removed and remains in place to define the respective pillars. Two
or more pillars are left protruding within the backside trench in
the vicinity of the inlet channels for a corresponding nozzle
chamber.
According to another aspect of the invention, an alternative
fabrication process is used to from the pillars. After the thin
film structure is applied, ink feed holes are etched into the thin
film structure down into the substrate. Material for an orifice
layer then is deposited into the holes and onto the thin film
structure. A firing chamber then is etched into the orifice layer.
During the etching of the firing chamber material is removed from
the ink feed holes. At another step, a trench is etched into the
backside of the wafer in the vicinity of the ink feed holes. After
the trench is formed, a conforming layer of photoimagable material
is spun into the trench along the backside of the substrate and
thin film structure. At another step, an alignment and exposure
process are performed to define an array of pillars within the
trench. After the exposure, a developing process is performed to
remove unwanted material and leave the pillars in place. The
pillars are formed within the trench. Such pillars are formed on
the underside of the thin film structure or on the backside of the
substrate. In an alternative procedure, the pillars are formed
before the orifice layer is deposited and the nozzle chamber is
formed. One advantage of the photoimaging methodology embodiment is
that the pillars can be formed to precise size and shape at desired
locations.
According to another aspect of the invention, the pillars are
formed prior to the step of applying the thin film structure to the
printhead substrate. Pits are etched into the wafer at one step. At
another step the pits are filled with a backside etchant-resistant
material. The substrate then is planarized and fabrication
continues with the deposition of the thin film layer and the
orifice layer. The firing chamber, inlet channels and backside
trench then are etched. During etching of the backside trench the
etchant-resistant material filling the pits remains. Such material
protrudes within the trench as the pillars. Two or more pillars are
left protruding within the backside trench in the vicinity of inlet
channels for a corresponding nozzle chamber.
One advantage of the invention is that pillars form a barrier
`reef` which keeps particles away from ink feed holes of nozzle
chambers. Thus, fluid is able to flow into the nozzle chambers even
in the presence of particles. Another advantage of the pillars is
that ink drop weight is substantially unaffected and overshoot
during refill is slightly reduced. A slight decrease in refill
frequency is evident, however. These and other aspects and
advantages of the invention will be better understood by reference
to the following detailed description taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded view of a portion of a conventional inkjet
printhead;
FIG. 2 is a partial perspective view of a portion of an inkjet pen
including a printhead fabricated according to a method embodiment
of this invention;
FIG. 3 is a planar view of a substrate in process after deposition
of a thin film structure;
FIG. 4 is a planar view of a substrate in process after etching of
pillar openings;
FIG. 5 is a planar view of a substrate in process after deposition
of an orifice layer;
FIG. 6 is a planar view of a substrate in process after etching of
a nozzle firing chamber;
FIG. 7 is a planar view of a fabricated substrate portion after
etching a trench and revealing the pillars;
FIG. 8 is a planar view of a substrate in process for an
alternative method of this invention;
FIG. 9 is a planar view of the substrate in process of FIG. 8 after
applying a photoimagable material into a backside trench;
FIG. 10 is a planar view of a fabricated substrate portion for the
alternative method of this invention;
FIG. 11 is a perspective view of the underside of a portion of the
fabricated printhead of FIG. 2 or 10;
FIG. 12 is a planar view of a fabricated substrate portion for a
variation of the alternative method of this invention;
FIG. 13 is a planar view of a substrate in process after etching
pillar openings according to another alternative method of this
invention;
FIG. 14 is a planar view of the substrate in process after
depositing material into the openings of FIG. 13;
FIG. 15 is a planar view of the substrate in process of FIG. 14
after applying the thin film structure and etching inlet channel
openings;
FIG. 16 is a planar view of the substrate in process after
deposition of an orifice layer;
FIG. 17 is a planar view of the substrate in process after etching
out a nozzle firing chamber and the inlet channel openings;
FIG. 18 is a planar view of a fabricated substrate portion after
etching a trench and revealing the pillars; and
FIG. 19 is a planar view of a substrate in process after deposition
of a thin film structure and etching of openings according to
another alternative method of this invention;
FIG. 20 is a planar view of the substrate in process of FIG. 19
after depositing an orifice layer;
FIG. 21 is a planar view of the substrate in process of FIG. 20
after etching a nozzle firing chamber;
FIG. 22 is a planar view of a fabricated substrate portion after
etching a trench and revealing the pillars of FIG. 21;
FIG. 23 is a planar bottom view of the substrate portion of FIG. 22
taken along line 23--23; and
FIG. 24 is a block diagram of an inkjet printing system according
to an embodiment of this invention;
DESCRIPTION OF SPECIFIC EMBODIMENTS
Overview
FIG. 1 shows a portion of a conventional inkjet printhead 10
including a plurality of inkjet nozzle printing elements 11, formed
on a substrate 12. Each nozzle 11 includes a barrier inlet channel
14 with a resistor 16 situated at one end of the channel 14 within
a firing chamber 15. The barrier inlet channel 14 and firing
chamber 15 are formed in a barrier layer 17 made of a
photopolymerizable material which is appropriately masked and
developed to form a desired patterned opening. A pair of
projections 24 are formed in the walls of the barrier layer 17 at
the entrance to each inlet channel 14, separated by a width to
define the inlet channel width.
Ink (not shown) is introduced from an ink feed channel 18 at the
opposite end of the inlet channel 14 away from the resistor 16. The
ink feed channel 18 passes through the substrate 12 and is provided
with a continuous supply of ink from an ink reservoir (not shown)
located beneath the substrate 12. Associated with each resistor 16
is a nozzle opening 20, located near the resistor 16 in the
adjacent orifice plate 22.
A plurality of elliptical pillars 26 are included in the barrier
layer 17 along the edge of the ink feed channel 18 near the
entrance of the inlet channels 14. The pillars 26 are formed during
the processing of the barrier layer 17, and thus are formed
concurrently with the inlet channels 14 and firing chambers 15.
Each pillar is the same height as the barrier layer 17. The major
axis of each pillar 26 is perpendicular to the ink flow from feed
channel 18 into the inlet channels 14. The pillars 26 serve to
filter out internal particles from the ink reservoir before the
particles reach the inlet channels 14 and possibly clog one or more
inlet channels 14.
FIG. 2 shows a portion of an inkjet pen 28 having a fully
integrated thermal (FIT) inkjet printhead 30. The FIT printhead 30
is formed by a substrate 34, a thin film structure 36 and an
orifice layer 38, and includes a plurality of nozzle printing
elements 31. The substrate 34 includes a front surface and an
opposing back surface. Formed on the front surface are a plurality
of firing chambers 42. Formed into the back surface is an ink feed
channel 50 that is in fluid communication with the firing chamber
42 through inlet channels 44.
The thin film structure 36 includes various passivation,
insulation, resistive and conductive layers applied to the
substrate 34. A resistor 40 is formed in the thin film structure 36
for each nozzle printing element 31. Associated with each printing
element 31 is the firing chamber 42, one or more ink inlet channels
44, and an outlet orifice 46.
Ink I originating from a reservoir 48 is introduced into the firing
chamber 42 from an ink feed channel 50 and the inlet channels 44.
The substrate 34 also includes a plurality of barrier members 32
positioned to prevent particles P from reaching the inlet channels
44 or the firing chambers 42. In a preferred embodiment, the
barrier members 32 are pillars which are positioned in the ink feed
channel 50 adjacent to each of the inlet channels 44. Preferably,
the pillars 32 are formed on a back surface of the substrate and
extend in a direction substantially opposite to the flow direction
of ink through the inlet channels 44.
For typical particle sizes, it was found in simulation that ink
drop weight remains essentially the same when the barriers 32 are
included. It also was found that ink refill overshoot was slightly
reduced as the pillars appear to provide additional damping. Ink
refill frequency, however, decreased slightly as it takes a
slightly longer period to refill the nozzle firing chambers 42. The
height of the pillars 32 may vary. These experimental results were
achieved in an exemplary embodiment in which a lower portion of the
firing chamber 42 is 42 microns.times.26 microns with a height of 9
microns, and the upper portion is 16 microns in diameter and 3
microns thick. Corresponding inlets 44 are ovular at 7 microns by
22 microns, while the resistor 40 is 7 microns by 14 microns. With
pillars of either 6 microns or 12 microns in height, particles for
achieving the experimental results were 13 microns and 16 microns.
Of course, one skilled in the art will appreciate that the specific
dimensions of the firing chamber 42, inlets 44, resistor 40 and
pillars 32 may vary.
Method of Fabrication--Pillars Formed with Orifice Material
Referring to FIG. 3, a semiconductor wafer 34 (e.g., silicon) is
processed to receive a thin film structure 36. The thin film
structure 36 includes various passivation, insulation, resistive,
and conductive layers applied to the wafer 34 using known
semiconductor fabrication processes (e.g., deposition,
photoimaging, etching, and planarizing processes). An array of
resistors 40 is formed in the thin film structure 36 including
wiring lines for carrying currents to energize the resistors
40.
After the thin film structure 36 is applied, a plurality of
openings are etched into the thin film structure 36 and wafer 34.
For example, a photoresist and masking process are performed to
define a mask for the openings. An exposure and developing process
followed by the etching process results in a plurality of openings
as shown in FIG. 4. In one embodiment both pillar openings 54 and
inlet channel openings 56 are formed during a common etching
process. In another embodiment, separate etching processes are
performed to etch the pillar openings 54 to one depth and the inlet
openings 56 to another depth. In one embodiment the pillar openings
54 are formed within the inlet channel opening to a deeper depth of
the substrate 34.
Referring to FIG. 5, an orifice layer 38 is deposited to fill in
the openings 54, 56 and overlay the thin film structure 36. A
deposition process is used which assures that the deposited
material conforms to the shape of the openings 54, 56. At another
step as shown in FIG. 6, the firing chamber is etched from the
orifice layer 38. During this etching step, the material filling
the inlet openings 56 is removed. In a preferred embodiment,
photodefinable material is applied and exposed to enable the
etching process to define the firing chamber and etch out the
material filling the inlet openings. In another embodiment, the
firing chamber 42 is formed by first applying a mandrel to the thin
film structure 36 before applying the orifice layer 38. The mandrel
defines the shape of the firing chamber. The orifice layer is
applied around the mandrel. The mandrel also fills the inlet
openings 56 (rather than the orifice layer material). The mandrel
material then is etched away to leave the firing chamber 42 and
inlet openings 56.
At another step, a trench 50 is etched into the backside of the
wafer 34. The etching process leaves the orifice layer material in
what previously (see FIG. 4) were the pillar openings 54. Such
material now defines the pillars 32. The etching process removes
the substrate material exposing the inlet openings, which now
define the inlet channels 44. The end result is a trench 50 having
a plurality of pillars 32. Ink flows from the reservoir into the
trench to the inlet channels 44. Particles inadvertently flowing
with the ink are blocked by the pillars 32. The pillars 32 prevent
such particles from blocking an inlet channel 44. Thus, ink flows
into a nozzle chamber 42 even in the presence of a nearby
particle.
Alternative Method of Fabrication--Backside Spinning
According to an alternative method of forming the pillars 32, a
backside spinning process is used. At one step, the semiconductor
wafer 34 (e.g., silicon) is processed to receive the thin film
structure 36, as described above (see FIG. 3). Thereafter, the
pillars 32 may be formed or the firing chambers 42 may be formed.
Either can be formed first.
Referring to FIGS. 8-10, a method is described in which the firing
chambers 42 are formed before the pillars 32. After the thin film
structure 36 is applied, a plurality of inlet openings 44 are
etched into the thin film structure 36 and wafer 34 (like in the
FIG. 4 embodiment, but without the pillar openings 54). For
example, a photoresist and masking process are performed to define
a mask for the openings. An exposure and developing process
followed by the etching process results in the plurality of
openings 44 (as for openings 56 shown in FIG. 4). At another step,
the orifice layer 38 is deposited into the openings 44 and onto the
thin film structure 36 (similar to the process of FIG. 5). The
firing chamber 42 then is etched from the orifice layer as
described above for the prior embodiment of FIG. 6. The orifice
material is removed from the openings 44 in the same step. At
another step, a trench 50 is etched into the backside of the wafer
34 as shown in FIG. 8. FIG. 8 shows the substrate in process after
the firing chamber 42 and the trench 50 are formed.
Referring to FIG. 9, a conformable photoimagable material 52 then
is spun onto the backside of the wafer 34 within the trench 50. At
another step a masking alignment and exposure process is performed
to define where the pillars are to occur. Referring to FIG. 10, a
developing process then removes the unwanted photoimagable material
52 leaving material 52 only where the pillars 32 are located. Such
remaining material 52 defines the pillars 32. One benefit of this
imaging method of forming the pillars is that it is easy and simple
to design pillars to a desired shape and size. FIG. 11 shows the
underside of a fabricated inkjet printhead 30. Ink flows from a
reservoir into the trench 50 to the inlet channels 44. Particles
inadvertently flowing with the ink are blocked by the pillars 32.
The pillars 32 prevent such particles from blocking an inlet
channel 44. Thus, ink flows into a nozzle chamber 42 even in the
presence of a nearby particle. The pillars are formed in a pattern
that substantially surrounds each of the inlet channels 44.
Although the figures illustrate formation of the firing chamber 42
before the pillars 32, the firing chamber instead may be formed
after the pillars. For example, the backside trench 50 may be
etched and the pillars formed before an orifice layer is applied to
the thin film structure 36. The firing chamber then is formed in
the orifice layer 38.
Method of Fabrication--Pillar Material Deposited Before Thin Film
Layer
Referring to FIG. 13, pits or openings 54' are etched into in a
semiconductor wafer 34 (e.g., silicon) at one step. At subsequent
steps, a backside etchant-resistant material 60 is deposited into
the openings 54' and the substrate 34 is planarized (see FIG. 14).
Exemplary backside etchant-resistant materials 60 include, but are
not limited to, PSG, BPSG and Sol-Gels. At another step, the thin
film structure 36 is applied to the substrate 34 at the same
surface side as the filled in pits 54'. The thin film structure 36
includes various passivation, insulation, resistive, and conductive
layers applied to the wafer 34 using known semiconductor
fabrication processes (e.g., deposition, photoimaging, etching, and
planarizing processes). An array of resistors 40 is formed in the
thin film structure 36 including wiring lines for carrying currents
to energize the resistors 40.
After the thin film structure 36 is applied, a plurality of
openings 56 are etched into the thin film structure 36 and wafer
34. For example, a photoresist and masking process are performed to
define a mask for the openings. An exposure and developing process
followed by the etching process results in a plurality of openings
as shown in FIG. 15.
Referring to FIG. 16, an orifice layer 38 is deposited to fill in
the openings 56 and overlay the thin film structure 36. A
deposition process is used which assures that the deposited
material conforms to the shape of the openings 56. At another step
as shown in FIG. 17, the firing chamber 42 is etched from the
orifice layer 38. During this etching step, the material filling
the inlet openings 56 is removed. In a preferred embodiment,
photoresistive material is applied and exposed to enable the
etching process to define the firing chamber and etch out the
material filling the inlet openings.
At another step, a trench 50 is etched into the backside of the
wafer 34. Referring to FIG. 18, the etching process leaves the
etchant-resistant material 60 in what previously were the pillar
openings 54'. Such material now defines the pillars 32'. The
etching process removes the substrate material exposing the inlet
openings, which now define the inlet channels 44. In the embodiment
shown, a portion of the substrate 34 remains within the trench to
define the floor/roof of the trench 50. In another embodiment the
floor/roof of the trench 50 is the thin film structure 36. The end
result is a trench 50 having a plurality of pillars 32'. Ink flows
from the reservoir into the trench to the inlet channels 44 of
printing elements 31. Particles inadvertently flowing with the ink
are blocked by the pillars 32'. The pillars 32' prevent such
particles from blocking an inlet channel 44. Thus, ink flows into a
nozzle chamber 42 even in the presence of a nearby particle.
Method of Fabrication--Pillar Formed in Inlet Channel Opening
Referring to FIG. 19, a semiconductor wafer 34 (e.g., silicon) is
processed to receive a thin film structure 36. The thin film
structure 36 includes various passivation, insulation, resistive,
and conductive layers applied to the wafer 34 using known
semiconductor fabrication processes (e.g., deposition,
photoimaging, etching, and planarizing processes). An array of
resistors 40 is formed in the thin film structure 36 including
wiring lines for carrying currents to energize the resistors 40.
After the thin film structure 36 is applied, a plurality of inlet
channel openings 56" are etched into the thin film structure 36 and
wafer 34. For example, a photoresist and masking process are
performed to define a mask for the openings. An exposure and
developing process followed by the etching process results in a
plurality of openings as shown in FIG. 19.
Referring to FIG. 20, an orifice layer 38 is deposited to fill in
the openings 56" and overlay the thin film structure 36. A
deposition process is used which assures that the deposited
material conforms to the shape of the openings 56". At another step
as shown in FIG. 21, the firing chamber 42 is etched from the
orifice layer 38. During this etching step, the a portion of the
material filling the inlet openings 56" is removed, while leaving
material in place to serve as the pillars. In a preferred
embodiment, photodefinable material is applied and exposed to
enable the etching process to define the firing chamber 42 and etch
out the material filling the inlet openings 56", while leaving in
the material for the pillars. In an exemplary photodefinition
process, one dosage is used to define the orifice layer material to
be left in place, while a second dosage is used to define the
orifice layer material to be removed. The development/etching step
then removes the orifice layer material to create the nozzle
chamber and ink inlet channel, while leaving the pillars. A method
for creating a nozzle chamber by such a development process is
described in commonly assigned U.S. patent application Ser. No.
09/033,987 filed Mar. 3, 1998 for "Direct Imaging Polymer Fluid Jet
Orifice," of Chen at al., the content of which is incorporated
herein by reference and made a part hereof.
At another step, a trench 50 is etched into the backside of the
wafer 34. The etching process leaves the orifice layer material
defining the pillars 32" (see FIGS. 22 and 23). The pillars 32"
extend from the orifice layer at one border of the firing chamber
42 through the inlet channel openings 44 into the trench 50. The
etching process removes the substrate material exposing the inlet
openings 44 and the pillars 32". The end result is a trench 50
having a plurality of pillars 32". Ink flows from the reservoir
into the trench 50 to the inlet channels 44. Particles
inadvertently flowing with the ink are blocked by the pillars 32".
The pillars 32" prevent such particles from blocking an inlet
channel 44. Thus, ink flows into a nozzle chamber 42 even in the
presence of a nearby particle.
Printing System
Referring to FIG. 24, a thermal inkjet printing system 100 includes
an inkjet printhead assembly 112, an ink supply assembly 114, a
mounting assembly 116, a media transport assembly 118, a housing
120 and an electronic controller 122. The inkjet printhead assembly
112 is formed according to an embodiment of this invention, and
includes one or more printheads having a plurality of inkjet
nozzles 31 which eject ink onto a media sheet M. The printhead
assembly 112 receives ink from the ink supply assembly 114. The ink
supply assembly 114 includes a reservoir 115 for storing the ink.
The ink supply assembly 114 and printhead assembly 112 form either
a one-way ink delivery system or a recirculating ink delivery
system. For the recirculating ink delivery system, ink flows from
the reservoir into the printhead assembly. Some of the ink travels
into printhead dies and nozzle chambers, while other portions of
ink return to the ink reservoir.
In some embodiments the ink supply assembly 114 and inkjet
printhead assembly 116 are housed together in an inkjet pen or
cartridge. In other embodiments the ink supply assembly 114 is
separate from the inkjet printhead assembly 112 and feeds ink to
the printhead assembly through an interface connection, such as a
supply tube. For either approach the ink supply may be removed,
replaced and/or refilled. For example, in an inkjet pen having an
internal reservoir, the pen may be disassembled and the internal
reservoir removed. A new, filled reservoir then is placed within
the pen, and the pen reassembled for re-use. Alternatively, the
prior reservoir may be refilled and reinstalled in the pen or
filled in place without removal from the pen (an in some
embodiments without even disassembling the pen). In some
embodiments there is a local reservoir within the pen along with a
larger reservoir located separate from the pen. The separate
reservoir serves to refill the local reservoir. In various
embodiments, the separate reservoir and/or the local reservoir may
be removed, replaced and/or refilled.
The inkjet printhead assembly 112 is mounted relative to the
housing 120 to define a print zone 119 adjacent to the printhead
nozzles 31 in an area which is to receive the media sheet M. The
media sheet M is moved into the print zone 119 by the media
transport assembly 118. The mounting assembly 116 positions the
printhead assembly 112 relative to the media transport assembly
118. For a scanning type inkjet printhead assembly, the mounting
assembly 116 includes a carriage for moving the printhead assembly
112 relative to a media transport path to scan the printhead
assembly 112 relative to the media sheet. For a non-scanning type
inkjet printhead assembly, the mounting assembly 116 fixes the
inkjet printhead assembly 112 at a prescribed position along the
media transport path.
The electronic controller 122 receives documents, files or other
data 121 to be printed from a host system, such as a computer.
Typically, a print job is sent to the inkjet printing system 100
along an electronic, infrared, optical or other information
transfer path. The print job includes data and one or more commands
or command parameters. The electronic controller 122 includes
memory for temporarily storing the data. The electronic controller
122 provides timing control for firing respective inkjet nozzles 31
to define a pattern of ejected ink drops which form characters,
symbols or other graphics on the media sheet M. The pattern is
determined by the print job data and print job commands or command
parameters.
Upon activation of a given firing resistor 40 (see FIG. 2), ink
within the surrounding nozzle chamber 42 is ejected through the
nozzle opening 46 onto a media sheet M. The electronic controller
122 selects which firing resistors 40 are active at a given time by
activating corresponding drive signals to heat the corresponding
firing resistors 40. In one embodiment logic circuits and drive
circuits forming a portion of the controller 122 are mounted to the
substrate 34 of the printhead assembly 112. In an alternative
embodiment logic circuitry and drive circuitry are located off the
printhead assembly 112.
Meritorious and Advantageous Effects
One advantage of the invention is that pillars form a barrier
`reef` which keep particles away from ink feed holes of nozzle
chambers. Thus, fluid is able to flow into the nozzle chambers even
in the presence of particles. Another advantage of the pillars is
that ink drop weight is substantially unaffected and overshoot
during refill is slightly reduced.
Although a preferred embodiment of the invention has been
illustrated and described, various alternatives, modifications and
equivalents may be used. For example, although the trench 50 is
shown in FIGS. 8-10 as being etched through the substrate 34 to the
thin film structure 34 with the pillars 32, 32" formed adjacent to
the thin film structure 34, the trench 50 need not be etched all
the way through the substrate 34, as shown in FIG. 12. For example,
the pillars 32 may be formed adjacent to the remaining substrate
material using the methods described above for FIGS. 8-10.
Similarly, the trench 50 of FIGS. 2 and 7 not be etched all the way
through the substrate 34. In such embodiment the pillars 32 and
openings 44 extend through the thin film structure 36 and an
underlying portion of the substrate 34, which defines the
floor/roof of the trench 50. Similarly, the trench 50 of FIG. 23
not be etched all the way through the substrate 34. In such
embodiment the pillars 32" and openings 44 extend through the thin
film structure 36 and an underlying portion of the substrate 34,
which defines the floor/roof of the trench 50. Therefore, the
foregoing description should not be taken as limiting the scope of
the inventions which are defined by the appended claims.
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